1. Field of the Invention
The present invention relates to surface wave sensor apparatuses capable of detecting a target detection substance by changes in mass loading, and in particular, the present invention relates to a surface wave sensor apparatus suitable for detecting a target detection substance in a liquid.
2. Description of the Related Art
Various sensors have been proposed for detecting a substance contained in liquid. For example, in Japanese Unexamined Patent Application Publication No. 2001-102905, an in-liquid substance detection sensor detecting a substance in liquid using surface acoustic waves is disclosed.
FIG. 9 is a schematic front sectional view illustrating the in-liquid substance detection sensor described in Japanese Unexamined Patent Application Publication No. 2001-102905.
In this drawing, an in-liquid substance detection sensor 102 is dipped into a solution 101 containing a target detection substance. The in-liquid substance detection sensor 102 includes a surface wave device. That is, the in-liquid substance detection sensor 102 includes a rectangular plate-shaped piezoelectric substrate 103, an input IDT electrode 104 spaced from one side of the piezoelectric substrate 103 by a predetermined distance, and an output IDT electrode 105. Between the input IDT electrode 104 and the output IDT electrode 105, a film 106 is provided for absorbing a target detection substance. When an AC voltage is applied across the input IDT electrode 104 herein, surface acoustic waves are generated in the piezoelectric substrate 103. The surface acoustic waves propagate toward the output IDT electrode 105. Then, from the output IDT electrode 105, an electric signal due to the propagated surface waves is derived. Since the film 106 absorbs the target detection substance, the existence of the target detection substance changes the load applied on the surface of the piezoelectric substrate 103. Accordingly, the propagated surface acoustic waves are changed, so that the output derived from the output IDT electrode 105 is varied due to the existence of the target detection substance, enabling the presence and the density of the target detection substance to be detected.
However, in the measuring method using the in-liquid substance detection sensor 102, the in-liquid substance detection sensor 102 must be dipped into a liquid 101. Hence, when a small amount of the liquid 101, which is a target object, is only prepared, there has been a problem that the substance contained in the liquid 101 cannot be detected.
Also, even when a large amount of the liquid 101 is prepared, if the liquid is expensive, a problem of high measuring cost may arise.
In addition, since the liquid 101 adheres to regions other than the region where the surface acoustic waves propagate, i.e., regions where electrode pads and bonding wires connected to the IDT electrodes 104 and 105 are arranged, there also has been a problem that electric characteristics are changed, so that detection accuracies are deteriorated in the in-liquid substance detection sensor 102.
On the other hand, in Japanese Unexamined Patent Application Publication No. H10-41776 and Japanese Unexamined Patent Application Publication No. 2001-102905, as shown in front sectional views of FIGS. 10 and 11, surface acoustic wave apparatuses are disclosed. The surface acoustic wave apparatuses described in Japanese Unexamined Patent Application Publication No. H10-41776 and Japanese Unexamined Patent Application Publication No. 2001-102905 define a resonator and a filter utilizing electric characteristics of a surface acoustic wave device, and are not used for substance detection.
As shown in FIG. 10, a surface wave apparatus 201 includes a base substrate 202 and a frame 203 fixed on the base substrate 202. The base substrate 202 and the frame 203 are made of ceramics such as alumina. Terminal electrodes 204 and 205 are arranged to extend from the top surface of the base substrate 202 to the bottom surface thereof. The terminal electrodes 204 and 205 lead to the region surrounded with the frame 203, and in the region surrounded with the frame 203, an anisotropic conductive sheet 206 is laminated on the terminal electrodes 204 and 205.
On the anisotropic conductive sheet 206, a surface acoustic wave device 207 is stacked and on the surface acoustic wave device 207, an elastic sheet 208 is laminated. Then, a lid 209 is fixed on the upper surface of the frame 203 so as to press the elastic sheet 208. Hence, the electrode on the bottom surface of the surface acoustic wave device 207 is to be securely connected, due to an elastic force of the elastic sheet 208, to the terminal electrodes 204 and 205 with the anisotropic conductive sheet 206 therebetween.
On the other hand, as shown in FIG. 11, in a surface acoustic wave apparatus 251 described in Japanese Unexamined Patent Application Publication No. 2001-102905, on the bottom surface of a base substrate 252, external electrodes 253 and 254 are formed. Through-hole conductors 255 and 256 are arranged to lead to the bottom surface of the base substrate 252 from the upper surface thereof so as to be electrically connected to the external electrodes 253 and 254, respectively. On the upper surface of the base substrate 252, terminal electrodes 257 and 258 are arranged so as to be electrically connected to the upper ends of the through-hole conductors 255 and 256, respectively. To the terminal electrodes 257 and 258, a surface acoustic wave device 259 is electrically connected with metallic bumps 260 and 261, respectively. In the surface acoustic wave device 259, through-hole conductors 263 and 264 are formed within a piezoelectric substrate 262. First ends of the through-hole conductors 263 and 264 are electrically connected to the metallic bumps 260 and 261, respectively. The upper ends of the through-hole conductors 263 and 264 are electrically connected to electrodes, such as an IDT 266, formed on the upper surface of the piezoelectric substrate 262, respectively.
In order to achieve the electrical connection by the bumps 260 and 261 and to bond the surface acoustic wave device 259 on the base substrate 252, a die-bonding member 267 herein is provided between the surface acoustic wave device 259 and the base substrate 252.
In the in-liquid substance detection sensor 102 described in Japanese Unexamined Patent Application Publication No. 2001-102905, as mentioned above, it must be dipped into the liquid 101 and when a small amount of the liquid 101 is only prepared, the substance contained in the liquid 101 cannot be detected. In addition, since the liquid 101 adheres to regions other than the region where the surface waves propagate, i.e., regions where electrode pads and bonding wires are arranged, there has been also a problem of insufficient detection accuracies.
On the other hand, in the surface acoustic wave apparatus 201 described in Japanese Unexamined Patent Application Publication No. H10-41776, the electrical connection between the terminal electrodes 204 and 205 on the base substrate 202 and the surface wave device 207 is made by the anisotropic conductive sheet 206. However, the surface acoustic wave apparatus 201 does not form a surface wave sensor apparatus. That is, the surface acoustic wave device 207 is only accommodated within an enclosed space surrounded by the base substrate 202, the frame 203, and the lid 209, and it is not intended to be used as the surface wave sensor apparatus and for detecting a detection substance contained in a liquid.
Also, in the surface acoustic wave apparatus 251, the apparatus is filled with the die-bond member 267 in a state of the metallic bumps 260 and 261 respectively being abutted by the through-hole conductors 263 and 264, so that the conjugation has been made by curing the die-bond member 267. Thus, since the die-bond member 267 is fluid before curing, it must be handled with care, so that there has been a problem of complicated bonding.
Also, in the surface acoustic wave apparatus 251, the surface acoustic wave device 259 is sealed in a region surrounded by the base substrate 252 and a cap member 271, and it is not intended to be used as a surface wave apparatus such as an in-liquid substance detection sensor.
As described above, the surface acoustic wave apparatuses described in Japanese Unexamined Patent Application Publication No. H10-41776 and Japanese Unexamined Patent Application Publication No. 2001-102905 disclose structural examples in that the surface acoustic wave device is electrically connected to electrodes on the base substrate. However, these surface acoustic wave apparatuses cannot be used for detecting a substance contained in a liquid.